Make Save Incremental avoid overwriting files and to be disabled on new files that haven't been saved

o Save incremental will use an auxiliary letter (a to z) and append it to the filename whenever it finds
an existing version with the same name.
o If the name of the file already included an incremental version with letters (i.e.: file_005b) it will
respect the letter and continue saving with it.
o Save incremental will be disabled on new files, it will become enabled when the file has been
saved at least once.